We investigate the design for a scattering with angular limitation in projection electron-beam lithography (SCALPEL) based electron projection system with a demagnification of -4. By a "field-flip" process we can construct a doubler in which the magnetic field has a flat feature in most of the optic column but opposite sign at two sides connected by a sharp transition region. Such a theoretical model can give a near zero chromatic aberration of rotation and much smaller field curvature and astigmatism. Compared with the conventional doublet, the total image blur caused by aberrations at 1/root 2 mm off-axis distance and 1.5 mrad semiangle aperture at the mask side is about only 24 nln for a column length of 400 mm. A shorter column, less than the current 400 mm, is also favored for further reducing the total aberration. These guarantee that we can choose a much larger aperture angle (compared with present 0.5 mrad) and beam current density in such a SCALPEL projection system to achieve higher throughput while still maintaining current resolution. A practical issue for possible magnetic lens design is also discussed.